In various heat changers or condensers in power plants, chemical plants, ships, etc. copper alloy tubes have broadly been used as heat exchanger or condenser tubes, such as tubes of so-called special brass which is a brass containing additionally aluminum, arsenic, silicon, etc., or tubes of so-called cupro-nickel alloy composed of copper, nickel, iron, and manganese. Those heat exchanger tubes are vulnerable to some sorts of corrosion or erosion on the inner surface thereof because of their utilizing of brackish water or sea water for cooling the heat exchangers. Corrosion morphology is mainly divided into two forms of either erosion corrosion and pitting corrosion; the former is apt to be caused at the inlet of the tube or places of blockage with foreign matters where turbulence takes place often and the latter occurs all over the inner surface of the tube when polluted brackish or sea water is used for cooling. Corrosion products are simultaneously accumulated to deteriorate the overall heat transfer coefficient within the heat exchangers.
On the other hand an experimental knowledge that deposits of iron oxide in those heat exchanger tubes are helpful in preventing corrosion (the term is used in a broad sense containing erosion unless otherwise stated) of the inner surface of the tubes has contributed greatly to the corrosion resistance of the tube by spreading the practice of injecting ferrous ions artificially into the cooling water. This corrosion resistant phenomenon is chiefly due to the function of restraining cathodic reaction, by a film of ferric hydroxide formed on the inner surface of the tube, in the corrosion reaction. This method can not, however, be said to be an industrially settled stable corrosion preventing technology at the present stage, because the formation of the film of ferric hydroxide still largely depends on various conditions such as extent of pollution of cooling water, whether the disinfection treatment to the water by chlorine is carried out or not, quality of water for example water temperature, pH value of water, amount of ferrous ions injected, distance from the ferrous ions injection point to the heat exchanger tube, flowing speed of the cooling water in the tube, etc. Even in a case where the film of ferric hydroxide is once formed in the tube, far weaker sticking force of the film than the shearing force of an increased turbulent flow, which may take place around the blockage in the tube by shell or other foreign matters contained in the cooling water, is a great fault of this method to be a truly effective anti-corrosion film. Too much expectation of stable corrosion resistance results in formation of too thick film which often degrades the heat transfer of the tube, an essential function thereof, below the allowable limit value. In many plants such as condensers in the power plants, even a cleaning means for removing surplus or excess of film can recently be seen. As a matter of fact such an ideal film removing method as to restore the heat transferring capability sufficiently, while preventing exposure of the ground or base metal, can not be found. In many plants either the heat transference or conductivity or the corrosion resistance is actually sacrificed to some extent.